Acquisition of Sirius Group - Purchase price calculation (Details) - Sirius Group $ / shares in Units, $ in Millions	Feb. 26, 2021 USD ($) $ / shares shares
Business Acquisition [Line Items]
Sirius Group shares acquired for cash	$ 100.4
Fair value of the replaced Sirius Group equity awards attributable to pre-combination services	37.5
Transaction fee reimbursement	8.0
Total purchase price	$ 1,079.8
Common shares
Business Acquisition [Line Items]
Common Shares issued by SiriusPoint (in shares) \| shares	58,331,196
SiriusPoint share price as of February 26, 2021 (in dollars per share) \| $ / shares	$ 10.21
Equity interests issued	$ 595.6
Series A preference shares
Business Acquisition [Line Items]
Common Shares issued by SiriusPoint (in shares) \| shares	11,720,987
Equity interests issued	$ 40.8
Series B preference shares
Business Acquisition [Line Items]
Equity interests issued	200.0
Merger warrants
Business Acquisition [Line Items]
Equity interests issued	53.4
Private warrants
Business Acquisition [Line Items]
Equity interests issued	7.3
Sirius Group Public Warrants
Business Acquisition [Line Items]
Equity interests issued	2.6
Upside Rights
Business Acquisition [Line Items]
Equity interests issued	6.5
CVRs
Business Acquisition [Line Items]
Equity interests issued	27.0
CVR waiver restricted shares
Business Acquisition [Line Items]
Equity interests issued	$ 0.7

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